Vocabulary Terms Cell division Chromatid Centromere Interphase Cell cycle Mitosis Prophase Centriole Spindle Metaphase Anaphase Telophase Cytokinesis Cyclin Cancer

10-1 Cell Growth

There are limits to cell growth… The larger a cell becomes …

…the more demands the cell places on its DNA …and the more trouble the cell has moving nutrients & cell wastes across the cell membrane.

In eukaryotes, when the cell is small, the info stored in the DNA meets all the cell’s needs. But as a cell increases in size, it usually doesn’t have extra copies of DNA available. An “information crisis” will occur.

The rate at which food, oxygen and water exchange takes place depends on the surface area of the cell. The rate of production of waste products, however, depends on the cell’s volume.

Volume is NOT area Volume increases more rapidly than surface area as a cell grows in size. Think of a town with a quickly increasing population but only 1 main road!

Daughter Cells To solve the “info crisis”, before cell division occurs (while still in interphase), the cell replicates, or copies, all of its DNA. Each daughter cell will get a complete set of information. Cell division also solves the problem of increasing size by reducing cell volume. Each daughter cell has an increased ratio of surface area to volume. Now the cell is more efficient.

10-2 Cell Division

Where is DNA located ? 1. Inside nucleus 2. Arranged as chromosomes (in mitosis)

Chromosomes In eukaryotic cells, the genetic info that is passed from generation to generation is carried by chromosomes. Chromosomes are made up of DNA and proteins. The cells of every organism have a specific number of chromosomes. –Fruit flies: 8 –Humans: 46 –Carrot: 18

Chromosomes (cont’d) Chromosomes are only visible during cell division- otherwise dispersed in form of chromatin. Once replicated are in form of “sister” chromatids. They are attached to each other by centromeres. In mitosis, the sisters separate, with one part of the pair going to each cell.

Duplicated Chromosome (Late Interphase): Sister Chromatids Centromere

The Cell Cycle (the life of a cell) During the cell cycle, a cell –Grows –Prepares for division –Divides to form two daughter cells –Begins the cell cycle again

Cell Cycle 24 hours “G” or Growth 1 phase “S” or DNA Synthesis Growth 2 “M” or Mitosis phase //////

Events of the Cell Cycle G 1 : phase of activity in which cells do most of their growing. –Cells increase in size –Synthesize new proteins and organelles S: chromosomes are replicated and the synthesis of DNA molecules takes place. Now committed to rest of cycle. G 2 : shortest phase, when organelles and molecules of cell division are produced. Ready for M. M: mitosis phase

Interphase, Mitosis & Cytokinesis Interphase: the cell does its regular jobs of making needed proteins Mitosis: the cell nucleus divides Cytokinesis: the cytoplasm (or cell juice with cell parts) divides

Interphase Normal metabolic activities Most commonly viewed state DNA= chromatin

Late Interphase Prepares for mitosis DNA doubles=Sister chromatids Centrioles double in animals

Why do cells divide by Mitosis ? Growth & Repair Reproduction of single-celled organisms under optimal conditions constant environment Amoeba Reproducing

Cells dividing by Mitosis……. Identical to original cell Same chromosome # Identical chromosome makeup

Mitosis Biologists divide this process into 4 phases: –Prophase –Metaphase –Anaphase –Telophase

Prophase First and longest phase (50-60% of mitosis) The centrioles separate and take up position on opposite sides of the nucleus. Centrioles are fanlike microtubular structure that helps separate the chromosomes, which attach to these fibers.

Prophase Nuclear membrane disappears Doubled DNA = condensed (coiled more tightly) Un-needed nucleolus disappears

Spindle & spindle fibers : Pull apart the sister chromatids

Metaphase The chromosomes line up across the center of the cell. Microtubules connect the centromere of each chromosome to the poles of the spindle.

Metaphase Chromosomes line up mid- cell Facing inward Microtubules conntect centromere to each of the two poles.

Anaphase The centromeres that join the sister chromatids split, causing the sister chromatids to separate and become individual chromosomes. Chromosomes continue to move until they have separated into two groups near the poles of the spindle.

Anaphase

Plant Anaphase

Telophase The chromosomes, which were distinct and condensed, begin to disperse into a tangle of dense material. Nuclear envelope re-forms Spindle begins to break apart Nucleolus becomes visible in each daughter cell. Mitosis is complete but cell division has yet to take place.

Telophase

Animal Telophase

Cytokinesis: cell’s cytoplasm divides & splits apart

Cytokinesis This is division of the cytoplasm. Usually occurs at the same time as telophase. In animals, cell membrane draws in until cell is pinched into 2 parts. Each part has its own nucleus and organelles. In plants, they need a cell wall, so a cell plate forms between the divided nuclei, and a cell wall begins to appear there.

10-3 Regulating the Cell Cycle Knowing When to Stop Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new.

1. How do you think the body repairs an injury, such as a cut on a finger? 2. How long do you think this repair process continues? 3.What do you think causes the cells to stop the repair process?

Contact Inhibition When normal cells come into contact with other cells, they respond by not growing. If cells are removed from the center, the bordering cells will divide to fill.

Cell Cycle Regulators Hunt & Kirschner (1980s): cells in mitosis contain protein that when injected into nondividing cell, stimulated mitotic spindle to form. Called this protein cyclin.

Contact Inhibition Video eQC7k8

Cyclins Regulate the timing of the cell cycle in eukaryotic cells. Other regulating proteins also exist.

Internal Regulators Allow cell cycle to proceed only when certain processes have happened inside cell For example, only after chromosomes are duplicated, cell proceed into M phase. Another example is cell waiting in anaphase until all chromosomes are attached to spindle.

External Regulators Direct cells to speed up or slow down cell cycle. Growth factors speed up (embryonic development, wound healing) Cell surface regulators- when one cell touches another, signal given to slow down or stop cycle.

Cancer Cancer cells do not obey the ordinary signals that regulate cell growth. As a result, they form masses of cells called tumors that can damage surrounding tissues.

Cancerous cells …… Cycle too fast 2. Divide into more than two cells 3. No contact inhibition Masses of cells = “tumors” Benign- not destructive Malignant- potentially lethal